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题目目录</h2> <ol><li><a href="#q1">JavaScript有哪些方法定义对象</a></li> <li><a href="#q2">常见的兼容性问题</a></li> <li><a href="#q3">说说你对promise的了解</a></li> <li><a href="#q4">你觉得jQuery源码有哪些写的好的地方</a></li> <li><a href="#q5">vue,react,angular</a></li> <li><a href="#q6">Node的应用场景</a></li> <li><a href="#q7">谈谈你对AMD，CMD的理解</a></li> <li><a href="#q8">哪些操作会造成内存泄漏</a></li> <li><a href="#q9">web开发中会话跟踪的方法有哪些</a></li> <li><a href="#q10">介绍js的基本数据类型</a></li> <li><a href="#q11">介绍js有哪些内置对象</a></li> <li><a href="#q12">说几条写Javascript的基本规范</a></li> <li><a href="#q13">JavaScript有几种类型的值</a></li> <li><a href="#q14">JavaScript创建对象的几种方式</a></li> <li><a href="#q15">eval是做什么的</a></li> <li><a href="#q16">null,undefined的区别</a></li> <li><a href="#q17">[&quot;1&quot;,&quot;2&quot;,&quot;3&quot;].map(parseInt)的答案是多少</a></li> <li><a href="#q18">JavaScript代码中&quot;use strict&quot;;是什么意思</a></li> <li><a href="#q19">JSON的了解</a></li> <li><a href="#q20">js延迟加载的方式有哪些</a></li></ol> <h3 id="q1">1. JavaScript有哪些方法定义对象</h3> <ul><li>对象字面量：var obj={};</li> <li>构造函数:var obj=new Object()</li> <li>Object.create():var obj=Object.create(Object.protype)</li></ul> <h3 id="q2">2. 常见的兼容性问题</h3> <ul><li><p>png24位的图片在IE6浏览器出现背景，解决方案做成PNG8</p></li> <li><p>浏览器默认margin和padding不同，加上通配符*{margin:0,padding:0}来统一，但是效率低，一般如下解决</p> <div class="language-css line-numbers-mode"><pre class="language-css"><code><span class="token selector">body,ul,li,ol,dt,dd,form,input,h1,h2,h3,h4,h5,h6,p</span><span class="token punctuation">{</span>
    <span class="token property">padding</span><span class="token punctuation">:</span>0<span class="token punctuation">;</span>
    <span class="token property">margin</span><span class="token punctuation">:</span>0<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div></li> <li><p>IE下，event对象有x，y属性，但是没有pageX，pageY属性</p></li> <li><p>Firefox下，event对象有pageX,pageY属性，但是没有x，y属性</p></li></ul> <h3 id="q3">3. 说说你对promise的了解</h3> <ul><li>Promise有四种状态
<ul><li>pending：初始状态</li> <li>fulfilled：成功态</li> <li>rejected：失败态</li> <li>settled：Promise已被fulfilled或rejected，且不是pending</li></ul></li> <li>fulfilled与rejected一起合称settled</li> <li>Promise对象来进行延迟和异步计算</li></ul> <h4 id="promise的构造函数"><a href="#promise的构造函数" class="header-anchor">#</a> Promise的构造函数</h4> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> promise<span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Promise</span><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">resolve<span class="token punctuation">,</span>reject</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    
    <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">...</span><span class="token punctuation">)</span><span class="token punctuation">{</span>  <span class="token comment">// success</span>
       <span class="token function">resolve</span><span class="token punctuation">(</span>result<span class="token punctuation">)</span>
       <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span> <span class="token comment">// fail</span>
           <span class="token function">reject</span><span class="token punctuation">(</span><span class="token function">Error</span><span class="token punctuation">(</span>errMessage<span class="token punctuation">)</span><span class="token punctuation">)</span>
       <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><ul><li>promise实例拥有then方法（具有then方法的对象，通常称为thenable）
<ul><li>promise.then(onFulfilled,onRejected)</li> <li>接收两个函数作为参数，一个在fulfilled的时候被调用，一个在rejected的时候被调用，接收参数future,onFulfilled对应resolve，onRejected对应reject</li></ul></li></ul> <h3 id="q4">4. 你觉得jQuery源码有哪些写的好的地方</h3> <ul><li>jQuery源码封装在一个匿名函数的自执行环境中，有助于变量的全局污染，然后通过传入window对象参数，使window对象作为局部变量使用，好处是当jQuery中访问window对象时，就不用将作用域链退回到顶层作用域了，从而可以更快的访问window对象，同样，传入undefined参数，可以缩短查找undefined时的作用域链</li> <li>jQuery将一些原型属性和方法封装在了jquery.prototype中，为了缩短名称，又赋值给了jquery.fn，</li> <li>jQuery有一些数组和对象经常能够用到，jQuery将其保存为局部变量以提高访问速度</li> <li>jQuery实现的链式调用可以节约代码，所返回的都是同一对象，可以提高代码效率</li></ul> <h3 id="q5">5. vue,react,angular</h3> <ul><li>vue.js一个用于创建web交互页面的库，是一个精简的MVVM，通过双向数据绑定把View层和Modal层链接了起来。实际的DOM封装和输出格式都被抽象为了Directives，和Filters</li> <li>AngularJs是一个比较完善的前端MVVM框架，包含模板，数据双向绑定，路由，模块化，服务，依赖注入，模块功能强大丰富</li> <li>react仅仅是View层是facebook公司，推出一个用于构建UI的库，可以实现服务端渲染，使用了virtual dom，性能好</li></ul> <h3 id="q6">6. Node的使用场景</h3> <ul><li>特点
<ul><li>JavaScript运行环境</li> <li>依赖chrome v8引擎</li> <li>事件驱动</li> <li>非阻塞IO</li> <li>单线程，单进程</li></ul></li> <li>优点
<ul><li>高并发</li></ul></li> <li>缺点
<ul><li>只支持单核CPU，不能充分使用CPU</li> <li>可靠性低，代码某个环节崩溃，整个系统都崩溃</li></ul></li></ul> <h3 id="q7">7.谈谈你对AMD，CMD的理解</h3> <ul><li><p>CommonJs是服务器端模块的规范，Node.js采用了这个规范，模块加载是同步的，Amd规范则是异步的，允许指定回调函数</p></li> <li><p>AMD推荐的风格是返回一个对象作为模块对象，CommonJS的风格通过module.exports或exports的属性赋值来达到保留模块对象的目的</p></li></ul> <h4 id="es6模块-commonjs-amd-cmd"><a href="#es6模块-commonjs-amd-cmd" class="header-anchor">#</a> es6模块 CommonJS,AMD,CMD</h4> <ul><li>CommonJs的规范中，每个JavaScript文件就是一个独立的模块上下文（module content）,在这个上下文默认创建的属性都是私有的，也就是说，在一个文件定义的变量（包括函数和类），都是私有的，对其他文件不可见的</li> <li>CommonJS是同步加载模块，在浏览器中会出现堵塞情况，所以不适用</li> <li>AMD异步，需要定义define方式</li> <li>es6一个模块就是一个独立的文件，该文件内部所有变量，外部无法获取，如果你希望外部能够读取模块内部的某个变量，就必须使用export关键字输出该变量，es6还可以导出类，方法，自动适用严格模式</li></ul> <h3 id="q8">8.哪些操作会造成内存泄漏</h3> <ul><li>内存泄漏指任何对象在你不在拥有或需要它之后任然存在</li> <li>setTimeout的第一个参数使用字符串而非函数的话，会引发内存泄漏</li> <li>闭包，控制台日志，循环</li></ul> <h3 id="q9">9.web开发中会话跟踪的方法有哪些</h3> <ul><li>cookie</li> <li>session</li> <li>url重写</li> <li>隐藏input</li> <li>ip地址</li></ul> <h3 id="q10">10.介绍js的基本数据类型</h3> <ul><li>Undefined</li> <li>Null</li> <li>Boolean</li> <li>Number</li> <li>String</li></ul> <h3 id="q11">11.介绍js有哪些内置对象</h3> <ul><li>Object是JavaScript中所有对象的内置对象</li> <li>数据封装类对象：Object，Array，Boolean，Number，String</li> <li>其他对象：Function，Argument，Math，Date，RegExp,Error</li></ul> <h3 id="q12">12.说几条JavaScript的基本规范</h3> <ul><li>不在同一行声明多个变量</li> <li>使用<code>===或!==</code>来比较true/false或者数值</li> <li>使用对象字面量替代new Array这种形式</li> <li>不要使用全局函数</li> <li>Switch语句必须带有default分支</li> <li>if使用大括号</li> <li>for  in循环一个使用var关键字明确限定作用域，从而避免作用域污染</li></ul> <h3 id="q13">13.Javascript有几种类型的值</h3> <ul><li>栈：原始数据类型（Undefined，Null，Boolean，Number，String）</li> <li>堆：引用数据类型（对象，数值，函数）</li> <li>两种类型存储位置不同</li> <li>原始数据类型直接存储栈中简单数据段，占据空间少，大小固定，属于频繁使用数据，放在栈中存储</li> <li>引用数据类型直接存储在堆（heap）,占据空间大，大小不固定，在栈内存存放指向堆内存的指针</li></ul> <p><img src="https://img2023.cnblogs.com/blog/3089561/202302/3089561-20230226095324349-1262090708.png" alt=""></p> <h3 id="q14">14.Javascript创建对象的几种方式</h3> <ul><li>对象字面量</li></ul> <div class="language-code line-numbers-mode"><pre class="language-text"><code>var person={...}
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li>function无参构造函数</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">Person</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">var</span> person<span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
    person<span class="token punctuation">.</span>name<span class="token operator">=</span><span class="token string">&quot;xxx&quot;</span><span class="token punctuation">;</span>
    person<span class="token punctuation">.</span><span class="token function-variable function">work</span><span class="token operator">=</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token function">aleat</span><span class="token punctuation">(</span><span class="token string">&quot;xxx&quot;</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

person<span class="token punctuation">.</span><span class="token function">work</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><ul><li>function构造函数</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">Pet</span><span class="token punctuation">(</span><span class="token parameter">name<span class="token punctuation">,</span>age<span class="token punctuation">,</span>hobby</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">this</span><span class="token punctuation">.</span>name<span class="token operator">=</span>name<span class="token punctuation">;</span><span class="token comment">//this作⽤域：当前对象</span>
 <span class="token keyword">this</span><span class="token punctuation">.</span>age<span class="token operator">=</span>age<span class="token punctuation">;</span>
 <span class="token keyword">this</span><span class="token punctuation">.</span>hobby<span class="token operator">=</span>hobby<span class="token punctuation">;</span>
 <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function-variable function">eat</span><span class="token operator">=</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
 <span class="token function">alert</span><span class="token punctuation">(</span><span class="token string">&quot;我叫&quot;</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>name<span class="token operator">+</span><span class="token string">&quot;,我喜欢&quot;</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>hobby<span class="token operator">+</span><span class="token string">&quot;,是个程序员&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">var</span> maidou <span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Pet</span><span class="token punctuation">(</span><span class="token string">&quot;⻨兜&quot;</span><span class="token punctuation">,</span><span class="token number">25</span><span class="token punctuation">,</span><span class="token string">&quot;coding&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//实例化、创建对象</span>
maidou<span class="token punctuation">.</span><span class="token function">eat</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//调⽤eat⽅法</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><ul><li>工厂模式（内置对象）</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> wcDog<span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Object</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
wcDog<span class="token punctuation">.</span>name<span class="token operator">=</span><span class="token string">&quot;xxx&quot;</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><ul><li>用原型方式创建</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">Dog</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>

<span class="token class-name">Dog</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span>name<span class="token operator">=</span><span class="token string">&quot;xxx&quot;</span>
<span class="token class-name">Dog</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">eat</span><span class="token operator">=</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>


</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><ul><li>用混合方式来创建</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">Car</span><span class="token punctuation">(</span><span class="token parameter">name<span class="token punctuation">,</span>price</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>name<span class="token operator">=</span>name<span class="token punctuation">;</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>price<span class="token operator">=</span>price<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token class-name">Car</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">sell</span><span class="token operator">=</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token function">alert</span><span class="token punctuation">(</span><span class="token string">&quot;我是&quot;</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>name<span class="token operator">+</span><span class="token string">&quot;，我现在卖&quot;</span><span class="token operator">+</span><span class="token keyword">this</span><span class="token punctuation">.</span>price<span class="token operator">+</span><span class="token string">&quot;万元&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">var</span> camry <span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Car</span><span class="token punctuation">(</span><span class="token string">&quot;凯美瑞&quot;</span><span class="token punctuation">,</span><span class="token number">27</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
camry<span class="token punctuation">.</span><span class="token function">sell</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><h3 id="q15">15.eval是做什么的</h3> <ul><li>把对应的字符串解析成js代码执行</li> <li>比秒使用eval，不安全，非常耗性能</li> <li>JSON字符串转换为JSON对象的时候可以用eval
<ul><li>var obj=eval('('+str+')')</li></ul></li></ul> <h3 id="q16">16.null,undefined的区别</h3> <ul><li>undefined表示不存在这个值</li> <li>undefined是一个表示无的原始值或说表示缺少值，就是此处应该有一个值，但是还没有定义。当尝试读取时会返回undefined</li> <li>变量声明了，没有被赋值，undefined</li> <li>null表示一个对象被定义，值为空值</li> <li>null：是一个对象（空对象）</li> <li>在验证null时，一定要使用<code>===</code>，因为<code>==</code>无法分别null和undefined</li></ul> <h3 id="q17">17.[&quot;1&quot;,&quot;2&quot;,&quot;3&quot;].map(parseInt)的答案是多少</h3> <ul><li>[1,NaN,NaN],因为parseInt，需要两个参数（val，radix），radix表示解析时用的参数</li> <li>map传了3个(element,index.array),对应radix不合法导致解析失败</li></ul> <h3 id="q18">18.JavaScript代码中&quot;use strict&quot;;是什么意思</h3> <ul><li>use strict是一种ECMAscript5 添加的（严格）运行模式，这种模式使得JavaScript在更严格的条件下运行，使js编码更加规范化的模式，消除JavaScript语法的一些不合理，不严谨，怪异之处</li></ul> <h3 id="q19">19.JSON的了解</h3> <ul><li>JSON（JavaScript Object Notation）是一种数据交换格式</li> <li>基于JavaScript的一个子集，数据格式简单，易于读写</li> <li>JSON字符串转换为JSON对象</li></ul> <div class="language-code line-numbers-mode"><pre class="language-text"><code>var obj=eval('('+str+')')

var obj=str.parseJSON()

var obj=JSON.parse(str)
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><ul><li>JSON对象转JSON字符串</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> last<span class="token operator">=</span>obj<span class="token punctuation">.</span><span class="token function">toJSONString</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token keyword">var</span> last<span class="token operator">=</span><span class="token constant">JSON</span><span class="token punctuation">.</span><span class="token function">stringify</span><span class="token punctuation">(</span>obj<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="q20">20.JS延迟加载的方式有哪些</h3> <ul><li>defer和async，动态创建DOM方式</li> <li>按需异步载入js</li></ul></div></div>  <div class="page-edit"><div class="edit-link"><a href="https://github.com/linxin1123/vuepress-blog/edit/master/docs/08.面试/02.前端面试/01.基础篇/06.Javascript(二)-cnblog.md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2023/02/26, 19:02:51</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/a3a48c/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">JavaScript(一)</div></a> <a href="/pages/552413/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">JavaScript(三)</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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